Inkjet ink

ABSTRACT

An inkjet ink for a glass substrate can enable formation of an aesthetic image with high concealability on the surface of the glass substrate. The inkjet ink disclosed here can include: an inorganic solid including an inorganic pigment that develops a color except for black and a glass frit; a monomer component having a photocuring property; and a photoinitiator. In the inkjet ink, a volume ratio of the inorganic solid in a case where an ink total volume is 100 volume % can be 35 volume % or less, a volume ratio of the inorganic pigment in the case where a total volume of the inorganic solid is 100 volume % can be 15 volume % or more and less than 90 volume %, and a volume ratio of the inorganic pigment to the photoinitiator can be 11 times or less.

TECHNICAL FIELD

The present disclosure relates to an inkjet ink. Specifically, thepresent disclosure relates to an inkjet ink for a glass substrate foruse in drawing an image on a transparent glass substrate. Thisapplication claims the benefit of priority to Japanese PatentApplication No. 2020-054527 filed on Mar. 25, 2020. The entire contentsof this application are hereby incorporated herein by reference.

BACKGROUND ART

Inkjet printing has been employed to date as a printing method fordrawing an intended image such as a pattern or characters on a printingtarget. Inkjet printing can draw an image precisely with a simplereasonable device, and thus, has been used in various fields. In recentyears, the use of inkjet printing has been studied in drawing an imageon an inorganic substrate such as a glass substrate, a ceramic substrate(e.g., a ceramic or a ceramic tile), or a metal substrate. Specifically,to draw an image such as a pattern or characters in the field ofinorganic substrates, handwriting or plate printing has beenconventionally employed. On the other hand, inkjet printing does notneed a skilled artisan technique such as handwriting and, unlike plateprinting, enables quick on-demand printing. Thus, inkjet printing hasattracted attention from the viewpoint of productivity improvement.

It is, however, difficult to apply the inkjet printing techniqueemployed in the fields of paper and cloth to the field of inorganicsubstrates without change. Inkjet printing in the field of inorganicsubstances has much room for improvement. For example, in a productusing an inorganic substrate (inorganic product), calcination can beperformed at 450° C. or more (e.g., 450° C. to 1200° C.) on an inorganicsubstance on which an image is drawn. In this calcination, if an inkjetink for paper or cloth is used, a pigment might be discolored (or fade)during the calcination. In view of this, an inkjet ink for use in aninorganic substrate requiring calcination (inorganic substrate inkjetink) needs to have a composition in which calcination is taken intoconsideration. Examples of the inorganic substrate inkjet ink includeinks described in, for example, Patent Documents 1 to 3. Unlike paperand cloth, an inorganic substrate does not absorb ink. Thus, as theinkjet ink for inorganic substrates, a photocurable ink including aphotocurable component (e.g., photocurable monomer) is generally used.

In inorganic substrates described above, a glass substrate, a ceramicsubstrate, and a metal substrate require different ink properties (e.g.,fixing property). In view of this, in the field of recent inorganicsubstrate inkjet inks, it has been investigated that an ink compositionis changed in further details depending on a printing target. Forexample, Patent Document 4 discloses an inkjet ink for a glass substrateas a printing target (glass substrate inkjet ink). The ink disclosed inPatent Document 4 is supposed to have high adhesion especially to aglass substrate because a cross-linking agent and a silicone resin havea siloxane bond.

CITATION LIST Patent Documents

Patent Document 1: WO2007/20779

Patent Document 2: JP2017-75251A

Patent Document 3: JP2009-154419A

Patent Document 4: JP2016-069390A

SUMMARY OF INVENTION Technical Problems

However, in the conventional technique described above, althoughadhesion to a glass substrate has been studied, aesthetic appearance ofan image formed by using the ink has been insufficiently studied.Specifically, in the case of a transparent glass substrate, if an imagedrawn on the surface of the glass substrate has high permeability (lowconcealability), the opposite side of the image is visible through thesubstrate. Thus, aesthetic appearance might be significantly impairedfor some type of the image.

It is therefore a main object of the present disclosure to provide aglass substrate inkjet ink enabling formation of an aesthetic image withhigh concealability on a surface of a glass substrate by inkjetprinting. It is another object of the present disclosure to provide amethod for producing a glass product using the glass substrate inkjetink.

Solution to Problem

In view of the foregoing problems, to form an image with highconcealability, the content of an inorganic pigment in an ink needs tobe increased. The ink with an increased amount of the inorganic pigment,however, has other problems, and thus, cannot be easily used.

First, the ink with an increased amount of the inorganic pigment has asignificantly increased viscosity and makes inkjet printing difficult.Consequently, a precise image cannot be drawn with this ink. Inventorsof the present disclosure assumed that the viscosity of an inkjet ink isaffected by the total amount of an inorganic solid including aninorganic pigment and a glass frit. Thus, the ink viscosity can bemaintained at a low level by reducing the amount of the glass frit inaccordance with an increase in the amount of the inorganic pigment tothereby reduce the total amount of the inorganic solid to a certainlevel or less. On the other hand, the glass frit is a component forfixing the inorganic pigment to the substrate surface. Therefore, whenthe content of the glass frit is excessively reduced, an image aftercalcination might fail to be fixed on the surface of the glasssubstrate. In view of these, the inventors of the present disclosureconceived that the “content ratio of the inorganic solid to the inktotal amount” and the “content ratio of the inorganic pigment to thetotal amount of the inorganic pigment” are adjusted so that an ejectionproperty in printing, concealability of an image after calcination, anda fixing property to the glass substrate are well harmonized at highlevels. The ink viscosity is directly affected not by the “weight” butby the “volume” of the inorganic solid. In view of this, in thetechnique disclosed here, the contents of the inorganic solid and theglass frit are defined in volume ratios.

Second, the ink with an increased amount of the inorganic pigment isdifficult to be cured and blurs after being printed on a glass substratesurface, and thus, fails to form a sharp image, disadvantageously. Theinventors of the present disclosure assumed that the sharpness decreasedue to ink blurring occurs because the increase in the content of theink pigment reduces light transmittance (i.e., increases concealability)so that supply of sufficient light amount to a photocuring component inthe ink is prevented, and thus, the ink is not cured immediately afterprinting. Based on this assumption, through an investigation of apreferable range of the inorganic pigment volume ratio to aphotoinitiator in which an ink is photo-cured with a small amount oflight, the inventors of the present disclosure found that blurring dueto a failure of curing of the ink can be prevented and a sharp image canbe formed by adjusting the volume ratio within a predetermined range.

An inkjet ink disclosed here has been made based on the foregoingfindings. The inkjet ink is a glass substrate inkjet ink for use indrawing an image on a transparent glass substrate. The inkjet inkincludes: an inorganic solid including an inorganic pigment and a glassfrit, the inorganic pigment being used for developing a color except forblack; a monomer component having a photocuring property; and aphotoinitiator. In the inkjet ink disclosed here, a volume ratio of theinorganic solid in a case where a total volume of the inkjet ink is 100volume % is 35 volume % or less, a volume ratio of the inorganic pigmentin the case where the total volume of the inorganic solid is 100 volume% is 15 volume % or more and less than 90 volume %, and a volume ratioof the inorganic pigment to the photoinitiator is 11 times or less.

As described above, in the inkjet ink disclosed here, the “volume ratioof the inorganic solid to the ink total amount,” the “volume ratio ofthe inorganic pigment to the total amount of the inorganic solid,” andthe “volume ratio of the inorganic pigment to the photoinitiator” areadjusted within predetermined ranges. Accordingly, an ejection propertyin printing, a photocuring property after printing, concealability of animage after calcination, and a fixing property to the glass substratecan be obtained at high levels. A black inorganic pigment has lowerlight transmittance than those of inorganic pigments of other colors,and thus, a necessary content of the photoinitiator in the black ink isdifferent from those in inks of other colors. Thus, the inkjet inkdisclosed here is directed to an ink using an inorganic pigment for acolor except for black.

In a preferred aspect of the inkjet ink disclosed here, the inorganicpigment is an inorganic pigment that develops a color of cyan, magenta,or yellow. Examples of the inorganic pigment that develops a colorexcept for black are three primary colors for subtractive process.

In a preferred aspect of the inkjet ink disclosed here, the volume ratioof the inorganic solid in the case where the total volume of the inkjetink is 100 volume % is 15 volume % or more and 30 volume % or less.Accordingly, an ejection property in printing, concealability of animage after calcination, and a fixing property to the glass substratecan be obtained at high levels.

In a preferred aspect of the inkjet ink disclosed here, the volume ratioof the inorganic pigment in the case where the total volume of theinorganic solid is 100 volume % is 25 volume % or more and 85 volume %or less. Accordingly, concealability after calcination and a fixingproperty to the glass substrate can be obtained at higher levels.

In a preferred aspect of the inkjet ink disclosed here, the volume ratioof the inorganic pigment to the photoinitiator is 10.7 times or less.Accordingly, concealability after calcination and a photocuring propertyafter printing can be obtained at higher levels.

In a preferred aspect of the inkjet ink disclosed here, the monomercomponent includes at least a monofunctional acrylate monomer includingone acryloyl group or one methacryloyl group in a molecule, amonofunctional N-vinyl compound monomer in which one vinyl group isbound to a nitrogen (N) atom of a nitrogen-containing compound, and apolyfunctional vinyl ether monomer including at least two vinyl ethergroups in a molecule. The use of the photocurable monomer componentincluding these three types of monomers enables drawing of an imagehaving a high fixing property to the surface of the printing target andhigh flexibility after fixing.

In the aspect including the three types of monomers, a volume ratio ofthe monomer component in the case where the total volume of the inkjetink is 100 volume % is 50 volume % or more and 75 volume % or less.Accordingly, a fixing property to the surface of the printing target andflexibility after fixing can be obtained at high levels, and an imagehaving a shiny gloss and high color developability after calcination canbe formed.

In another aspect of the present disclosure, a method for producing aglass product having a decoration part is provided. The method ofproducing a glass product includes the steps of: performing inkjetprinting on a surface of a glass substrate with the inkjet ink disclosedhere; applying ultraviolet rays to the surface of the glass substrateand curing the inkjet ink adhering to the surface of the glasssubstrate; and calcining the glass substrate at a maximum calcinationtemperature of 450° C. to 1200° C.

The method for producing the glass product disclosed here uses theinkjet ink disclosed here. Accordingly, inkjet printing can be performedwith a high ejection property so that a precise image can be printed onthe surface of the glass substrate. In addition, since the ink has ahigh photocuring property, adhesion of coating and blurring of an imageafter printing can be prevented so that a sharp image can be formed.Furthermore, since the image (decoration part) after calcination hasboth concealability and a fixing property at high levels, aestheticappearance can be maintained for a long period. That is, the productionmethod disclosed here can easily produce a glass product with anaesthetic image.

The present disclosure also provides a method for producing transferpaper for a glass substrate (hereinafter also referred to simply as“transfer paper”) to be used for a glass substrate. The method forproducing the transfer paper includes: performing inkjet printing on asurface of a mount with the inkjet ink disclosed here; and applyingultraviolet rays to the surface of the mount and curing the inkjet inkadhering to the surface of the mount.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a stirringmill for producing an inkjet ink.

FIG. 2 is an overall view schematically illustrating an example of aninkjet apparatus.

FIG. 3 is a cross-sectional view schematically illustrating an inkjethead of the inkjet apparatus in FIG. 2 .

DESCRIPTION OF PREFERRED EMBODIMENTS

A preferred embodiment of the present disclosure will be hereinafterdescribed. Matters not specifically mentioned in the description butrequired for carrying out the present disclosure can be understood asmatters of design variation of a person skilled in the art based onrelated art in the field. The present disclosure can be carried out onthe basis of the contents disclosed in the description and commongeneral knowledge in the field.

1. Inkjet Ink

An inkjet ink disclosed here is a glass substrate inkjet ink for use indrawing an image on a transparent glass substrate. The inkjet inkincludes at least an inorganic solid, a monomer component (photocurablemonomer component) having a photocuring property, and a photoinitiator.The components will be described below.

(1) Inorganic Solid

An inorganic solid is a component constituting a base material of animage (decoration part) after calcination, and includes an inorganicpigment and a glass frit.

(a) Inorganic Pigment

An inorganic pigment is added in order to develop an intended color on asubstrate surface after calcination. The inorganic pigment can include,for example, a metal compound. The inorganic pigment has high heatresistance. Thus, when a glass substrate to which an ink adheres iscalcined at 450° C. or more (e.g., 450° C. to 1200° C.), discoloration(fading) of the pigment can be prevented. Specific examples of theinorganic pigment include a composite metal compound including at leastone metal element selected from the group consisting of Cu, Mn, Zr, Ti,Pr, Cr, Sb, Ni, Co, Al, and Cd. Among these materials, a Zr-basedcomposite metal oxide (e.g., ZrSiO₄) including Zr as a main component ispreferably used from the viewpoint of heat resistance.

The technique disclosed here is directed to an ink using an inorganicpigment that develops a color except for black. This is because a blackinorganic pigment has a light transmittance lower than those ofinorganic pigments of other colors, and thus, a content of the blackinorganic pigment necessary for forming an image with highconcealability is different from those of other colors. The color of theinorganic pigment used in the inkjet ink disclosed here can be any colorexcept for black, and an intended color can be selected without anyparticular limitation. For example, in typical inkjet printing, inks ofthree primary colors for subtractive process, such as cyan, yellow, andmagenta, are used as inks except for black. In the case of using theZr-based composite metal oxide described above as the inorganic pigment,the Zr-based composite metal oxide is doped with predetermined metalelements so that inorganic pigments of the three colors describe abovecan be thereby obtained. For example, a Zr-based composite metal oxidefor cyan can be ZrSiO₄—V (vanadium), a Zr-based composite metal oxidefor yellow can be ZrSiO₄—Pr (praseodymium), and a Zr-based compositemetal oxide for magenta can be ZrSiO₄—Fe. Other examples of an inorganicpigment of a color except for the three colors described above includean inorganic pigment of white. As the white inorganic pigment, TiO₂,ZrO₂, ZnO, or ZrSiO₄, for example, is preferably used.

The inorganic pigment can be typically particulate. The particle size ofthe particulate inorganic pigment is preferably adjusted as appropriatein consideration of the diameter of an ejection orifice of an inkjetapparatus described later. If the particle size of the inorganic pigmentis excessively large, the ejection orifice might be clogged with theinorganic pigment so that an ink ejection property might decrease. Sincea typical diameter of an ejection orifice of an inkjet apparatus isabout 15 μm to 60 μm (e.g., 25 μm), the particle size of the inorganicpigment is preferably reduced such that a D₁₀₀ particle size (maximumparticle size) corresponding to a cumulative 100 particles % from asmaller particle size side is 5 μm or less (preferably 1 μm or less).The D₁₀₀ particle size can be a value measured based on a particle sizedistribution measurement by dynamic light scattering.

The inorganic pigment may be inorganic particles mixed and dispersed ina glass frit described later. The inorganic particles can be, forexample, nanometal particles. Example of the nanometal particles includenanogold particles, nanosilver particles, nanocopper particles,nanoplatinum particles, nanotitanium particles, and nanopalladiumparticles. The nanometal particles have specific optical features (e.g.,a strong light absorption band) in ultraviolet to visible ranges due tosurface plasmon resonance (SPR). For example, nanogold (Au) particlesabsorb light of a wavelength around 530 nm (e.g., green to light-bluelight) and develops bluish red (reddish violet) called “marron.” Thus,in the case of preparing an ink of red or violet, for example, nanogoldparticles are preferably used as nanometal particles. For example,nanosilver (Ag) particles absorb light of a wavelength around 420 nm(blue light) and develop yellow. Thus, in the case of preparing an inkof orange or yellow, for example, nanosilver particles are preferablyused as nanometal particles. In a preferred aspect, a D₅₀ particle sizeof nanometal particles is 5 nm or more, and typically 10 nm or more, forexample, 15 nm or more. In another preferred aspect, the D₅₀ particlesize of nanometal particles is generally 80 nm or less, and typically 50nm or less, for example, 30 nm or less. By setting the D₅₀ particle sizein the range described above, absorbance of nanometal particles at aspecific wavelength increases so that excellent color development can beachieved with a small amount of addition. In addition, a precise imagewith small color unevenness can be drawn.

(b) Glass Frit

A glass frit melts during calcination of a glass substrate to which anink adheres, and is then solidified while being cooled after thecalcination to thereby cause an inorganic pigment to be fixed to thesubstrate surface. A glass frit of the inkjet ink disclosed herepreferably includes a glass material that covers an inorganic pigmentafter cooling and develops a shiny gloss.

Examples of a glass material that can have such properties includeSiO₂—B₂O₃-based glass, SiO₂—RO (where RO is an oxide of a group-2element, e.g., MgO, CaO, SrO, or BaO; the same hereinafter)-based glass,SiO₂—RO—R₂O (where R₂O is an oxide of an alkali metal element, e.g.,Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, or Fr₂O, especially Li₂O; the samehereinafter)-based glass, SiO₂—B₂O₃—R₂O-based glass, SiO₂—RO—ZnO-basedglass, SiO₂—RO—ZrO₂-based glass, SiO₂—RO—Al₂O₃-based glass,SiO₂—RO—Bi₂O₃-based glass, SiO₂—R₂O-based glass, SiO₂—ZnO-based glass,SiO₂—ZrO₂-based glass, SiO₂—Al₂O₃-based glass, RO—R₂O-based glass, andRO—ZnO-based glass. The glass material may include one or morecomponents in addition to main components included in the designationsabove. The glass frit may include crystallized glass including crystalas well as typical amorphous glass.

In a preferred aspect, supposing the entire glass material is 100 mol %,SiO₂ occupies a half (50 mol %) or more of the material. A percentage ofSiO₂ can be generally 80 mol % or less. From the viewpoint of increasingmeltability of the glass frit, a component such as RO, R₂O, or B₂O₃ maybe added. In a preferred aspect, supposing the entire glass material is100 mol %, RO is 0 to 35 mol %. In another preferred aspect, supposingthe entire glass material is 100 mol %, R₂O is 0 to 10 mol %. In anotherpreferred aspect, supposing the entire glass material is 100 mol %, B₂O₃is 0 to 30 mol %.

In a preferred aspect, the glass material is constituted by amulti-component system including four or more components (e.g., five ormore components). Accordingly, physical stability of an image aftercalcination increases. For example, a component such as Al₂O₃, ZnO, CaO,or ZrO₂ may be added in a proportion of, for example, 1 mol % or more.Accordingly, chemical durability and abrasion resistance of thedecoration part can be increased. In a preferred aspect, supposing theentire glass material is 100 mol %, Al₂O₃ is 0 to 10 mol %. In apreferred aspect, supposing the entire glass material is 100 mol %, ZrO₂is 0 to 10 mol %.

In a preferred example of the glass frit disclosed here, supposing theentire glass material is 100 mol %, a glass frit includes borosilicateglass having the following composition with a mole ratio in terms ofoxide:

SiO₂ 40 to 70 mol % (e.g., 50 to 60 mol %);

B₂O₃ 10 to 40 mol % (e.g., 20 to 30 mol %);

R₂O (at least one of Li₂O, Na₂O, K₂O, or Rb₂O) 3 to 20 mol % (e.g., 5 to10 mol %);

Al₂O₃ 0 to 20 mol % (e.g., 5 to 10 mol %); and

ZrO₂ 0 to 10 mol % (e.g., 3 to 6 mol %).

A percentage of SiO₂ in the entire glass matrix of borosilicate glassmay be, for example, 40 mol % or more, and may be typically 70 mol % orless, for example, 65 mol % or less. A percentage of B₂O₃ in the entireglass matrix may be typically 10 mol % or more, for example, 15 mol % ormore, and may be typically 40 mol % or less, for example, 35 mol % orless. A percentage of R₂O in the entire glass matrix may be typically 3mol % or more, for example, 6 mol % or more, and may be typically 20 mol% or less, for example, 15 mol % or less. In a preferred aspect,borosilicate glass includes Li₂O, Na₂O, and K₂O as R₂O. A percentage ofLi₂O in the entire glass matrix can be, for example, 3 mol % or more and6 mol % or less. A percentage of K₂O in the entire glass matrix can be,for example, 0.5 mol % or more and 3 mol % or less. A percentage of Na₂Oin the entire glass matrix can be, for example, 0.5 mol % or more and 3mol % or less. A percentage of Al₂O₃ in the entire glass matrix may betypically 3 mol % or more, and may be typically 20 mol % or less, forexample, 15 mol % or less. A percentage of ZrO₂ in the entire glassmatrix may be typically 1 mol % or more, and may be typically 10 mol %or less, for example, 8 mol % or less.

Borosilicate glass may include other additional components. Examples ofthe additional components include, in the state of an oxide, forexample, BeO, MgO, CaO, SrO, BaO, ZnO, Ag₂O, TiO₂, V₂O₅, FeO, Fe₂O₃,Fe₃O₄, CuO, Cu₂O, Nb₂O₅, P₂O₅, La₂O₃, CeO₂, Bi₂O₃, and Pb₂O₃. Theadditional components may be included in a percentage of 10 mol % orless in total as a guide, supposing the entire glass matrix is 100 mol%.

Other examples of the glass frit disclosed here include a glass fritincluding a glass material 90 mol % or more of which has the followingcomposition with a mole ratio in terms of oxide, supposing the entireglass is 100 mol %:

SiO₂ 45 to 70 mol % (e.g., 50 to 60 mol %);

SnO₂ 0.1 to 6 mol % (e.g., 1 to 5 mol %);

ZnO 1 to 15 mol % (e.g., 4 to 10 mol %);

RO (at least one of BeO, MgO, CaO, SrO, or BaO) 15 to 35 mol % (e.g., 20to 30 mol %);

R₂O (at least one of Li₂O, Na₂O, K₂O, or Rb₂O) 0 to 5 mol % (e.g., 1 to5 mol %); and

B₂O₃ 0 to 3 mol % (e.g., 0 to 1 mol %).

A percentage of SiO₂ in the entire glass matrix of the glass materialhaving the above composition may be, for example, 50 mol % or more andmay be typically 65 mol % or less, for example, 60 mol % or less. Apercentage of SnO₂ in the entire glass matrix may be typically 0.5 mol %or more, for example, 1 mol % or more, and may be typically 5.5 mol % orless, for example, 5 mol % or less. A percentage of ZnO in the entireglass matrix may be typically 2 mol % or more, for example, 4 mol % ormore, and may be typically 12 mol % or less, for example, 10 mol % orless. A percentage of RO in the entire glass matrix may be typically 18mol % or more, for example, 20 mol % or more, and may be typically 32mol % or less, for example, 30 mol % or less. A percentage of R₂O in theentire glass matrix may be generally 0.1 mol % or more, for example, 1mol % or more, and may be, for example, 3 mol % or less. A percentage ofB₂O₃ in the entire glass matrix may be typically 1 mol % or less, forexample, 0.1 mol % or less.

The glass frit may include additional components except for thecomponents described above. Examples of the additional componentsinclude, in the form of, for example, an oxide, Ag₂O, Al₂O₃, ZrO₂, TiO₂,V₂O₅, FeO, Fe₂O₃, Fe₃O₄, CuO, Cu₂O, Nb₂O₅, P₂O₅, La₂O₃, CeO₂, and Bi₂O₃.The additional components may be included in a percentage of 10 mol % orless in total as a guide, supposing the entire glass matrix is 100 mol%.

A coefficient of linear thermal expansion (average coefficient of linearexpansion measured in a temperature range from 25° C. to 500° C. with athermomechanical analyzer; the same hereinafter) of the glass frit ispreferably 10.0×10⁻⁶K⁻¹ or less, for example. Accordingly, a differencein contraction factor between the glass frit and a decoration target(glass substrate) in calcination decreases so that the decoration partis less likely to suffer from separation or cracks. Although a yieldpoint of the glass frit is not limited to a specific temperature, andcan be, for example, 400° C. to 700° C. A glass transition point (Tgvalue based on differential scanning calorimetry; the same hereinafter)of the glass frit is not limited to a specific temperature, and can be,for example, 400° C. to 700° C.

The glass frit typically includes a particulate glass material. Theparticle size of the glass frit affects an ink viscosity, and thus, ispreferably adjusted as appropriate in consideration of an ejectionproperty from the inkjet apparatus. Specifically, if the ink includes aglass frit having a large particle size, the ejection orifice is likelyto be clogged and the ejection property might decrease. In view of this,the particle size of the glass frit is preferably controlled such thatthe maximum particle size (D₁₀₀ particle size corresponding to acumulative 100 particles % from a smaller particle size side) of theglass frit is 1 μm or less (preferably 0.85 μm or less).

(2) Photocurable Monomer Component

The inkjet ink disclosed here is a photocurable inkjet ink containing amonomer component having a photocuring property. The “photocurablemonomer component” herein refers to a material including at least onemonomer of resin that is typically in a liquid state and is polymerized(or cross-linked) to be cured upon application of light (e.g.,ultraviolet rays). As such a photocurable monomer component, a monomerthat can be used for a typical photocurable ink can be used without anyparticular limitation within the range where advantages of the presentdisclosure are not significantly impaired.

Preferred examples of the photocurable monomer component include aphotocurable monomer component including (a) monofunctional acrylatemonomer, (b) monofunctional N-vinyl compound monomer, and (c)polyfunctional vinyl ether monomer. The photocurable monomer componentincluding the monomers (a) through (c) has a high fixing property(photocuring property) to a printing target, and thus, can be preferablyused for various printing targets. The photocurable monomer componentsincluding the monomers (a) through (c) also has the advantage of highflexibility after photocuring, and thus, can be especially preferablyused for a printing target that needs to be bent in application (e.g.,transfer paper for an inorganic material).

(a) Monofunctional Acrylate Monomer

The monofunctional acrylate monomer is a compound including one anacryloyl group (CH₂═CHCOO—) or one methacryloyl group (CH₂═CCH₃COO—) ina molecule.

The monofunctional acrylate monomer has high dispersibility of aninorganic solid component and can suppress an increase in ink viscosity,and thus, can contribute to preparation of an ink having a preferableejection property. Among monomers having photocuring properties, themonofunctional acrylate monomer has a relatively low stiffness(relatively high flexibility) after photocuring.

From the viewpoint of further increasing the ejection property andflexibility, the volume ratio of the monofunctional acrylate monomer ina case where the total volume of the photocurable monomer component is100 volume % is preferably 40 volume % or more, more preferably 45volume % or more, and even more preferably 50 volume % or more, andespecially preferably 55 volume % or more, and is, for example, 60volume % or more. On the other hand, the monofunctional acrylate monomertends to have a relatively low photocuring property. Thus, from theviewpoint of obtaining a content of a monomer having a high photocuringproperty described later, the monofunctional acrylate monomer ispreferably 96 volume % or less, more preferably 90 volume % or less,even more preferably 85 volume % or less, and especially preferably 80volume % or less, and is, for example, 78 volume % or less.

Specific examples of the monofunctional acrylate monomer include benzylacrylate, annular trimethylolpropane formal acrylate, phenoxyethylacrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, methoxyethylacrylate, cyclohexyl acrylate, ethyl carbitol acrylate,(2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate, hydroxyethylacrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate,methyl(meth)acrylate, ethyl acrylate, propyl acrylate, butyl acrylate,pentyl acrylate, n-stearyl acrylate, butoxy ethyl(meth)acrylate,tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate,2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,t-butyl cyclohexyl (meth)acrylate, isoamyl acrylate, lauryl(meth)acrylate, octyl acrylate, isooctyl (meth)acrylate, isononylacrylate, decyl acrylate, isodecyl acrylate, tridecyl (meth)acrylate,isomyristylacrylate, isostearyl acrylate, 2-ethylhexyl acrylate,2-ethylhexyl-diglycol acrylate, 4-hydroxybutyl acrylate,methoxydiethylene glycol acrylate, methoxytriethylene glycol acrylate,ethoxydiethylene glycol acrylate, 2-(2-ethoxyethoxy)ethyl acrylate,2-ethylhexyl carbitol acrylate, and phenoxyethoxy ethyl acrylate. One ormore (meth)acrylate compounds may be used alone or in combination. Amongthese compounds, benzyl acrylate, phenoxyethyl acrylate, and annulartrimethylolpropane formal acrylate have especially high flexibilityafter photocuring, and thus, can favorably prevent occurrence of cracksin bending transfer paper.

(b) Monofunctional N-Vinyl Compound Monomer

The monofunctional N-vinyl compound monomer is a compound in which onevinyl group is bound to a nitrogen (N) atom of a nitrogen-containingcompound. The “vinyl group” herein refers to CH₂═CR¹— (where R1 is ahydrogen atom or an organic group). The monofunctional N-vinyl compoundmonomer has high extensibility, and thus, can suppress occurrence ofcracks in the drawn image. The monofunctional N-vinyl compound monomerhas a high photocuring property, and has the function of increasing afixing property to a surface of a printing target.

From the viewpoint of further increasing the fixing property, the volumeratio of the monofunctional N-vinyl compound monomer in the case wherethe total volume of the photocurable monomer component is 100 volume %is preferably 2 volume % or more, more preferably 3 volume % or more,even more preferably 4 volume % or more, and especially preferably 5volume % or more. On the other hand, when the monofunctional N-vinylcompound monomer is added, flexibility of the ink after curing tends todecrease. In view of this, in the case of using transfer paper for aninorganic substrate, for example, the content of the monofunctionalN-vinyl compound monomer is preferably reduced. From the viewpoint, thevolume ratio of the monofunctional N-vinyl compound monomer ispreferably 20 volume % or less, more preferably 17 volume % or less,even more preferably 15 volume % or less, and especially preferably 10volume % or less.

The N-vinyl compound monomer is expressed by, for example, the followingEquation (1):

CH₂═CR′—NR²R³  (1)

In Equation (1), R1 is an alkyl group with a hydrogen atom number and acarbon atom number of 1 to 4, a phenyl group, a benzyl group, or ahalogen group. Among these materials, an alkyl group with a hydrogenatom number and a carbon atom number of 1 to 4 is preferable, andhydrogen atoms are especially preferable. In addition, each of R² and R³can be a group selected from the group consisting of a hydrogen atom, analkyl group, an alkenyl group, an alkynyl group, an aralkyl group, analkoxy group, an alkoxyalkyl group, an alkylol group, an acetyl group(CH₃CO—), and an aromatic group that may have substituents. The R² andR³ may be the same or different from each other. The total number ofcarbon atoms in an alkyl group, an alkenyl group, an alkynyl group, anaralkyl group, an alkoxy group, an alkoxyalkyl group, an alkylol group,and an acetyl group that may have substituents can be 1 to 20. The alkylgroup, the alkenyl group, the alkynyl group, the aralkyl group, thealkoxy group, the alkoxyalkyl group, the alkylol group, and the acetylgroup that may have substituents can be a chain or annular, and ispreferably a chain. The aromatic group is an aryl group that may have asubstituent. The total number of carbon atoms in the aromatic group is 6to 36. Substituents that the alkyl group, the alkenyl group, the alkynylgroup, the aralkyl group, the alkoxy group, the alkoxyalkyl group, thealkylol group, the acetyl group, and the aromatic group can have,include halogen atoms such as a hydroxy group, fluorine atoms, andchlorine atoms. In Equation (1), R² and R³ may be joined together toform an annular structure.

Preferred examples of the monofunctional N-vinyl compound monomerinclude N-vinyl-2-caprolactam, N-vinyl-2-pyrrolidone,N-vinyl-3-morpholinone, N-vinylpiperidine, N-vinylpyrrolidine,N-vinylaziridine, N-vinylazetidine, N-vinylimidazole, N-vinylmorpholine,N-vinylpyrazole, N-vinylvalerolactam, N-vinylcarbazole,N-vinylphthalimide, N-vinylformamide, N-vinylacetamide,N-methyl-N-vinylformamide, and N-methyl-N-vinylacetamide. Among thesematerials, N-vinyl-2-caprolactam has a high photocuring property amongmonofunctional N-vinyl compound monomers and thus can more favorablyincrease a fixing property to the surface of a printing target.

(c) Polyfunctional Vinyl Ether Monomer

The polyfunctional vinyl ether monomer is a compound including at leasttwo vinyl ether groups in a molecule. The “vinyl ether group” hereinrefers to —O—CH═CHR1 (where R1 is a hydrogen atom or an organic group).The polyfunctional vinyl ether monomer including at least two vinylether groups has a high photocuring speed in UV irradiation and a highphotocuring property, and thus, can increase a fixing property to thesurface of a printing target. In addition, the polyfunctional vinylether monomer has low stiffness after curing among monomers having highphotocuring properties and has high flexibility.

From the viewpoint of obtaining both a fixing property to a printingtarget and flexibility after photocuring, the volume ratio of thepolyfunctional vinyl ether monomer in a case where the total volume ofthe monomer component is 100 volume % is preferably 2 volume % or more,more preferably 5 volume % or more, even more preferably 7 volume % ormore, especially preferably 10 volume % or more, and is, for example, 15volume % or more. On the other hand, if an excessive amount of thepolyfunctional vinyl ether monomer is added, the amount of addition ofthe monofunctional acrylate monomer decreases so that flexibility afterphotocuring tends to decrease. In view of this, the upper limit of thevolume ratio of the polyfunctional vinyl ether monomer is preferably 40volume % or less, more preferably 35 volume % or less, even morepreferably 30 volume % or less, especially preferably 25 volume % orless, and is, for example, 20 volume % or less.

Preferred examples of the polyfunctional vinyl ether monomer includeethylene glycol divinyl ether, diethylene glycol divinyl ether,triethylene glycol divinyl ether, tetraethylene glycol divinyl ether,polyethylene glycol divinyl ether, propylene glycol divinyl ether,dipropylene glycol divinyl ether, tripropylene glycol divinyl ether,polypropylene glycol divinyl ether, butanediol divinyl ether, neopentylglycol divinyl ether, hexanediol divinyl ether, nonanediol divinylether, and 1,4-cyclohexanedimethanol divinyl ether. Among thesematerials, diethylene glycol divinyl ether, triethylene glycol divinylether, and 1,4-cyclohexanedimethanol divinyl ether obtain both a fixingproperty to the substrate surface and flexibility after photocuring athigh levels, and thus, are especially preferable.

In the case of using the photocurable monomer component including themonomers (a) through (c), the volume ratio of the monomer component inthe case where the total volume of the inkjet ink is 100 volume % ispreferably 50 volume % or more, more preferably 52 volume % or more,even more preferably 58 volume % or more, and especially preferably 60volume % or more. Accordingly, a fixing property to the surface of aprinting target and flexibility after fixing can be achieved at higherlevels. From the viewpoints of obtaining a sufficient content of aninorganic solid and forming an image (decoration part) having a shinygloss and high color developability, the volume ratio of the monomercomponent is preferably 85 volume % or less, more preferably 80 volume %or less, even more preferably 75 volume % or less, and especiallypreferably 70 volume % or less.

(d) Other monomers

As described above, as the photocurable monomer components in the inkjetink disclosed here, monomer components that can be used for a typicalphotocurable inkjet ink are used without any particular limitation, andare not limited to the monomers (a) through (c) described above.

Examples of monomers other than the monomers (a) through (c) (othermonomers) include a polyfunctional acrylate monomer including at leasttwo acryloyl groups or methacryloyl groups in a molecule. Preferredexamples of the polyfunctional acrylate monomer include 1,9-nonanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, tricyclodecane dimethanol diacrylate, hydroxy pivalateneopentyl glycol diacrylate, triethylene glycol di(meth)acrylate,tetramethylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,3-butanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate, hexanedioldi(meth)acrylate, cyclohexane-1,4-dimethanol di(meth)acrylate,cyclohexane-1,3-dimethanol di(meth)acrylate, 1,4-cyclohexanedioldi(meth)acrylate, tetraethylene glycol di(meth)acrylate, pentaerythritoldi(meth)acrylate, dipentaerythritol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenolAEO 3.8-molar adduct diacrylate, trimethylolpropane tri(meth)acrylate,trimethylolethane tri(meth)acrylate, trimethylol octanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropanepolyethoxy tri(meth)acrylate, dipentaerythritol tri(meth)acrylate,dipentaerythritol propionate tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, sorbitol tri(meth)acrylate,ditrimethylolpropane tetra(meth)acrylate, pentaerythritol polyethoxytetra(meth)acrylate, pentaerythritol polyproxy tetra(meth)acrylate,sorbitol tetra(meth)acrylate, dipentaerythritol propionatetetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate,sorbitol penta(meth)acrylate, dipentaerythritol penta(meth)acrylate,dipentaerythritol hexa(meth)acrylate, and sorbitol hexa(meth)acrylate.

Examples of other monomers other than the polyfunctional acrylatemonomer include butyl vinyl ether, butyl propenyl ether, butyl butenylether, hexyl vinyl ether, ethylhexyl vinyl ether, phenyl vinyl ether,benzyl vinyl ether, phenylallyl ether, vinyl acetate, acrylamide,methacrylamide, trimethylolpropane tri((meth)acryloyloxypropyl) ether,tri((meth)acryloyloxyethyl) isocyanurate, and a bisphenol A diglycidylether acrylic acid adduct.

(3) Photoinitiator

The inkjet ink disclosed here includes a photoinitiator. Thephotoinitiator absorbs light to be activated, and generates reactioninitiators such as radical molecules and hydrogen ions. When thesereaction initiators act on photocurable monomers to thereby acceleratepolymerization reaction and cross-linkage reaction of the photocurablemonomers. That is, an ink that can be easily cured even with a smallamount of light can be prepared by increasing the content of thephotoinitiator. As the photoinitiator, a conventional photoinitiator canbe used without any particular limitation. Examples of thephotoinitiator include a radical-based photoinitiator such as analkylphenone-based photoinitiator and an acylphosphine oxide-basedphotoinitiator. Preferred examples of the alkylphenone-basedphotoinitiator include α-aminoalkylphenone-based photoinitiators (e.g.,2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, and2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone).Other examples of the alkylphenone-based photoinitiator includeα-hydroxyalkylphenone-based photoinitiators (e.g.,1-hydroxy-cyclohexyl-phenyl-ketone,2-hydroxy-2-methyl-1-phenyl-propane-1-one,1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, and2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propane-1-one).Among the photoinitiators described above, the α-aminoalkylphenone-basedphotoinitiators such as2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one have highreactivity to increase a curing speed of an ink and have a highthin-film curing property and a high surface hardening property, andthus, are especially preferably used.

(4) Other Components

The inkjet ink disclosed here may additionally include a known additive(e.g., a disperser, a polymerization inhibitor, a binder, or a viscosityadjuster) that can be used for an inkjet ink (typically, an inkjet inkfor a glass substrate and a photocuring inkjet ink) within the rangethat does not impair advantages of the present disclosure. The contentof the additive may be approximately set depending on a purpose of theadditive, and is not a feature of the present disclosure, and thus, willnot be described in detail.

(a) Disperser

The inkjet ink disclosed here may include a disperser. As a disperser, acation-based disperser is used, for example. The cation-based disperserefficiently adheres to the surface of an inorganic pigment by acid-basereaction, and thus, suppresses agglomeration of the inorganic pigment todisperse the inorganic pigment favorably unlike other dispersers such asa phosphoric acid-based disperser. Examples of the cation-baseddisperser include an amine-based disperser. The amine-based dispersercan prevent aggregation of an inorganic pigment due to steric hindranceand can stabilize the inorganic pigment. In addition, since the sameelectric charges can be applied to inorganic pigment particles,agglomeration of the inorganic pigment can also be favorably preventedin this respect. Accordingly, the viscosity of the ink can be reduced sothat printing performance can be significantly increased. Examples ofthe amine-based disperser include an aliphatic amine-based disperser anda polyester amine-based disperse, and DISPERBYK-2013 produced by BYKJAPAN KK, for example, is preferably used.

(b) Polymerization Inhibitor

The inkjet ink disclosed here may include a polymerization inhibitor.The addition of the polymerization inhibitor can suppress polymerizationand curing of the photocurable monomer component before use, and thus,the ink can be easily stored. As the polymerization inhibitor, amaterial conventionally used in the field of the photocurable inkjet inkcan be used without any particular limitation as long as the materialdoes not significantly reduce a photocuring property of the photocurablemonomer component including the monomers (a) through (c) described aboveand reduce advantages of the technique disclosed here. Examples of thepolymerization inhibitor include hydroquinone, methoquinone, di-t-butylhydroquinone, P-methoxyphenol, butyl hydroxytoluene, and nitrosaminesalt. Among components included in these inhibitors, N-nitrophenylhydroxylamine aluminum salt is especially preferable because of highstability in long-term storage.

(5) Contents of Components

The inkjet ink disclosed here is characterized by controlling (a) thevolume ratio of the inorganic solid to the ink total amount, (b) thevolume ratio of the inorganic pigment to the total amount of theinorganic solid, and (c) the volume ratio of the inorganic pigment tothe photoinitiator within predetermined ranges. These components willnow be described.

(a) Volume Ratio of Inorganic Solid to Ink Total Amount

First, in the inkjet ink disclosed here, the volume ratio of theinorganic solid in the case where the total volume of the inkjet ink is100 volume % is 35 volume % or less. The “volume of the inorganic solid”refers to the total volume of the inorganic pigment and the glass frit.As the volume of the inorganic solid increases, the ink viscosity tendsto increase. The inorganic pigment and the glass frit included in theinorganic solid can be of various types, and have various specificgravities. Thus, in this embodiment, not the “weight” but the “mass” ofthe inorganic solid is adjusted. Although described in detail later, theinkjet ink disclosed here includes an increased amount of an inorganicpigment in order to form an image with high concealability. Even such anink including a large amount of inorganic pigment can obtain a low inkviscosity suitable for inkjet printing (typically less than 110 Pas,preferably 70 Pas or less) by reducing the volume ratio of the inorganicsolid to the ink total amount to 35 volume % or less. From the viewpointof more favorably reducing the ink viscosity, the volume ratio of theinorganic solid is preferably 32 volume % or less, more preferably 30volume % or less, even more preferably 28 volume % or less, andespecially preferably 25 volume % or less. On the other hand, from theviewpoints of obtaining sufficiently high concealability aftercalcination and sufficiently high fixing property, the lower limit ofthe volume ratio of the inorganic solid is preferably 10 volume % ormore, more preferably 12 volume % or more, even more preferably 15volume % or more, and especially preferably 16 volume % or more.

(b) Volume Ratio of Inorganic Pigment to Total Amount of Inorganic Solid

Next, in the inkjet ink disclosed here, the volume of the inorganicpigment in the case where the total volume of the inorganic solid is 100volume % is adjusted to 15 volume % or more. By including a large amountof inorganic pigment in this manner, an image with high concealabilitycan be formed. From the viewpoint of forming an image with higherconcealability, the volume ratio of the inorganic pigment is preferably17.5 volume % or more, more preferably 20 volume % or more, even morepreferably 25 volume % or more, and especially preferably 27.5 volume %or more. On the other hand, if the volume ratio of the inorganic pigmentto the total amount of the inorganic solid is excessively increased, adecreased amount of the glass frit might reduce a fixing property of animage after calcination. From this viewpoint, the upper limit of thevolume ratio of the inorganic pigment is set to be less than 90 volume%. From the viewpoint of ensuring fixing of an image after calcination,the upper limit of the volume ratio of volume ratio of the inorganicpigment is preferably 85 volume % or less, more preferably 80 volume %or less, and especially preferably 70 volume % or less.

(c) Volume Ratio of Inorganic Pigment to Photoinitiator

In the technique disclosed here, even for an ink including an increasedamount of the inorganic pigment, the volume ratio of the inorganicpigment to the photoinitiator is defined in order to obtain appropriatephotocuring effect. An experiment conducted by the inventors of thepresent disclosure confirmed that even for inks each having the samevolume ratio of an inorganic solid and a photoinitiator, an ink having alarger volume of an inorganic pigment shows lower photocuring property.While there is no intention to limit the technique disclosed here, sucha phenomenon is supposed to be because an insufficient light amount issupplied to photocurable monomers in an ink having a high volume ratioof an inorganic pigment and has high concealability. On the other hand,in the inkjet ink disclosed here, the amount of addition of thephotoinitiator is defined in consideration of the volume ratio of theinorganic pigment that is a cause of decrease in photocuring property.Specifically, in the inkjet ink disclosed here, the volume ratio of theinorganic pigment to the photoinitiator is adjusted to 11 times or less.Accordingly, although a large amount of the inorganic pigment isincluded, sufficient photocuring is exhibited, and a sharp image withoutblurring can be formed. From the viewpoint of obtaining a more favorablephotocuring property, the volume ratio of the inorganic pigment to thephotoinitiator is preferably 10.7 times or less, more preferably 10times or less, and even more preferably 8.4 times or less. On the otherhand, the lower limit of the volume ratio of the inorganic pigment tothe photoinitiator is not specifically limited, and may be 0.3 times ormore, 1.1 times or more, 1.3 times or more, and 1.7 times or more.

As described above, in the inkjet ink disclosed here, (a) the volumeratio of the inorganic solid to the ink total amount, (b) the volumeratio of the inorganic pigment to the total amount of the inorganicsolid, and (c) the volume ratio of the inorganic pigment to thephotoinitiator are controlled within predetermined ranges. The inkjetink can obtain an ejection property in printing, a photocuring propertyafter printing, concealability of an image after calcination, and afixing property to a glass substrate at high levels, and thus, enableseasy production of a glass product with an aesthetic image.

2. Preparation of Inkjet Ink

A procedure of preparing (producing) the inkjet ink disclosed here willnow be described. The inkjet ink disclosed here can be prepared bymixing the materials described above in predetermined proportions andthen milling and dispersing the inorganic solid. FIG. 1 is across-sectional view schematically illustrating a stirring mill for usein production of an inkjet ink. The following description is notintended to limit the inkjet ink disclosed here.

First, in producing the inkjet ink disclosed here, the materialsdescribed above are weighed and mixed, thereby preparing slurry as aprecursor of the ink.

Next, with a stirring mill 100 as illustrated in FIG. 1 , stirring ofthe slurry and milling of an inorganic solid (an inorganic pigment and aglass frit) are performed. Specifically, milling beads (e.g., zirconiabeads with a diameter of 0.5 mm) are added to the slurry, and then theslurry is supplied to a stirring vessel 120 from a supply port 110. Thestirring vessel 120 houses a shaft 134 having a plurality of stirringblades 132. One end of the shaft 134 is attached to a motor (not shown),and the motor is driven to rotate the shaft 134 so that the slurry isstirred while being sent to a downstream side in a liquid feedingdirection A with the stirring blades 132. During the stirring, theinorganic solid is milled by the milling beads added to the slurry sothat the atomized inorganic solid is dispersed into the slurry.

The slurry sent to the downstream side in the liquid feeding direction Athen passes through a filter 140. Accordingly, the milling beads and anon-atomized inorganic solid are caught by the filter 140, and an inkjetink in which the atomized inorganic solid is sufficiently dispersed isejected from an ejection port 150. The pore size of the filter 140 atthis time is adjusted so that a maximum particle size of the inorganicsolid in the inkjet ink can be controlled.

3. Application of Inkjet Ink

Next, application of the inkjet ink disclosed here will be described. Asdescribed above, the inkjet ink disclosed here is used for drawing animage on a transparent glass substrate. The term of “being used fordrawing an image on a transparent glass substrate” herein is a situationincluding not only a state where the ink directly is caused to adhere tothe surface of the glass substrate but also a state where the ink iscaused to indirectly adhere to the surface of the glass substrate withan interposition of, for example, transfer paper. That is, the inkjetink disclosed here can be used for printing on glass substrate transferpaper (production of transfer paper) and printing on a glass substratesurface (production of a glass production).

(1) Production of Transfer Paper

A method for producing glass substrate transfer paper (printing methodfor drawing an image on the surface of transfer paper) with the inkjetink disclosed here will be described. FIG. 2 is an overall viewschematically illustrating an example of an inkjet apparatus. FIG. 3 isa cross-sectional view schematically illustrating an ink jet head of theinkjet apparatus in FIG. 2 .

The inkjet ink disclosed here is stored in inkjet heads 10 of the inkjetapparatus 1 illustrated in FIG. 2 . The inkjet apparatus 1 includes fourinkjet heads 10. The inkjet heads 10 store inks of four different colorsof black (K), cyan (C), yellow (Y), and magenta (M). The inkjet inkdisclosed here is stored in the inkjet heads 10 of cyan (C), yellow (Y),and magenta (M), except for black (K). The inkjet heads 10 are housed ina printing cartridge 40. The printing cartridge 40 is inserted in aguide shaft 20 and is configured to reciprocate along an axial directionX of the guide shaft 20. Although not shown, the inkjet apparatus 1includes a moving means for moving the guide shaft 20 in a verticaldirection Y. In this manner, the ink can be ejected from the inkjetheads 10 toward a desired position on a mount W of transfer paper.

The inkjet heads 10 illustrated in FIG. 2 are, for example, a piezoinkjet head as illustrated in FIG. 3 . Each of the piezo inkjet heads 10includes a storage 13 for storing ink in a case 12, and the storage 13communicates with an ejection part 16 through a liquid feeding path 15.The ejection part 16 has an ejection orifice 17 that is open to theoutside of the case 12, and includes a piezoelectric device 18 facingthe ejection orifice 17. In each of the inkjet heads 10, thepiezoelectric device 18 is caused to vibrate so that ink in the ejectionpart 16 is ejected from the ejection orifice 17 toward the mount W (seeFIG. 2 ).

The guide shaft 20 of the inkjet apparatus 1 illustrated in FIG. 2 isprovided with an UV irradiator 30. The UV irradiator 30 is disposedadjacent to the printing cartridge 40, moves together with reciprocationof the printing cartridge 40, and applies UV light to the mount V towhich the ink adheres. Accordingly, the ink is cured immediately afterthe ink adheres to the surface of the mount W, and thus, ink with asufficient thickness can be fixed to the surface of transfer paper(mount W).

As described above, in the inkjet ink disclosed here, the volume of theinorganic solid to the total volume of the inkjet ink is adjusted to 35volume % or less. Accordingly, a low ink viscosity can be maintained sothat ink can be accurately ejected from the ejection orifice 17, and aprecise image can be drawn on the surface of a printing target (transferpaper in this example). In addition, in the inkjet ink disclosed here,the volume ratio of the inorganic pigment to the photoinitiator isadjusted to 11 times or less. Accordingly, a high photocuring propertyis obtained so that ink after UV irradiation can be immediately curedand blurring of the ink can be prevented.

In producing the transfer paper, the photocurable monomer componentincluding the monomers (a) through (c) described above is preferablyused. Accordingly, an image (cured ink) having sufficient flexibilitycan be drawn, and thus, cracks in an image occurring in bending transferpaper can be prevented.

(2) Method for Producing Glass Product

Next, a method for producing a glass product with the inkjet inkdisclosed here will be described. The production method includes thestep of causing the inkjet ink disclosed here to adhere to a surface ofa glass substrate and the step of calcining the glass substrate.

A glass substrate produced by this method is not limited to a specificmethod as long as an image is formed on a surface of a glass substrate.For example, the glass product is not limited to everyday items such astable ware, windowpanes, and cooking appliances, and may be industrialitems such as electronic equipment and displays. The glass substrate asa printing target is not specifically limited, and a general glassmember can be used without any particular limitation. In considerationof a calcination process described later, a glass substrate having asoftening point of 500° C. or more, (more preferably 600° C. or more,even more preferably 700° C. or more) is preferably used. On the otherhand, the upper limit of the softening point of the glass substrate isnot limited to a specific temperature. For example, the upper limit ofthe softening point of the glass substrate may be 1600° C. or less,1200° C. or less, or 1000° C. or less

First, in the production method disclosed here, an inkjet ink is causedto adhere to a surface of a glass substrate. A technique for causing theink to the glass substrate is not specifically limited. The ink may becaused to adhere directly to the surface of the glass substrate with aninkjet apparatus or the ink may be caused to adhere indirectly with aninterposition of the transfer paper described above. In a case where theinkjet apparatus is used to cause the ink to adhere directly to thesurface of the glass substrate, the ink is preferably ejected toward thesurface of the glass substrate according to the same procedure as thatin the “production of transfer paper” described above.

In the production method disclosed here, the glass substrate to whichthe ink adheres is calcined in a condition in which a maximumcalcination temperature is set within a range of 450° C. to 1200° C.(preferably 500° C. to 1000° C., more preferably 550° C. to 850° C.).Accordingly, a resin component as a cured monomer is burnt, and a glassfrit in an inorganic solid melts. The glass substrate is cooled afterthe calcination so that the molten glass frit is solidified, and theinorganic pigment is fixed to a substrate surface. At this time, in theproduction method disclosed here, since the ink in which the volume ofthe inorganic pigment to the total volume of the inorganic solid isadjusted to 15 volume % or more, an aesthetic image with highconcealability can be formed. In addition, since the volume of theinorganic pigment to the total volume of the inorganic solid is adjustedto be less than 90 volume %, the inorganic pigment can be appropriatelyfixed to the surface of the glass substrate.

Test Examples

Test examples of the present disclosure will be described, but theseexamples are not intended to limit the present disclosure.

<Inkjet Ink>

In this test, 18 types of inkjet inks (Examples 1 through 18) eachincluding an inorganic solid, a photocurable monomer, and aphotoinitiator were prepared. Specifically, slurry was prepared bymixing materials in volume ratios shown in Tables 1 and 2, and subjectedto milling and dispersion with milling beads (zirconia beads with adiameter of 0.5 mm), thereby obtaining inks of Examples 1 through 18.The volume ratios in the tables are values in the case where the totalvolume of the ink is 100 volume %, except where otherwise specified. Inthe test examples, a disperser (produced by BYK JAPAN KK:DISPERBYK-2013) and a polymerization inhibitor (produced by FUJIFILMWako Pure Chemical Corporation: Q-1301 (N-nitroso-N-phenyl hydroxylaminealuminum)) were added as other additives. The volume ratios of theseadditives are also shown in Tables 1 and 2. The volume ratio of eachcomponent is a value rounded to the second decimal place.

In the inorganic solid in this test examples, “yellow” is a rutile-typetitania-based yellow inorganic pigment. “Cyan” is an inorganic pigmentof zircon-based cyan. “White” is a titania-based white inorganicpigment. “Glass frit” is borosilicate glass having a softening point of550° C.

The “photocuring component” in Tables 1 and 2 is a mixture of amonofunctional acrylate monomer, a monofunctional N-vinyl compoundmonomer, a polyfunctional acrylate monomer, and a polyfunctional vinylether monomer in a predetermined volume ratio. As the monofunctionalacrylate monomer, a mixture of isobornyl acrylate (produced by OSAKAORGANIC CHEMICAL INDUSTRY LTD.), benzyl acrylate (produced by OSAKAORGANIC CHEMICAL INDUSTRY LTD.), phenoxyethyl acrylate (produced byOSAKA ORGANIC CHEMICAL INDUSTRY LTD.), and annular trimethylolpropaneformal acrylate (produced by OSAKA ORGANIC CHEMICAL INDUSTRY LTD.) wasused. As the monofunctional N-vinyl compound monomer, N-vinylcaprolactam(produced by Tokyo Chemical Industry Co., Ltd.) was used. As thepolyfunctional acrylate monomer, 1,9-nonanediol diacrylate (produced byOSAKA ORGANIC CHEMICAL INDUSTRY LTD.) was used. As the polyfunctionalvinyl ether monomer, a mixture of triethylene glycol divinyl ether(produced by NIPPON CARBIDE INDUSTRIES CO., INC.), diethylene glycoldivinyl ether (produced by NIPPON CARBIDE INDUSTRIES CO., INC.), and1,4-cyclohexanedimethanol divinyl ether (produced by NIPPON CARBIDEINDUSTRIES CO., INC.) was used.

As the photoinitiator, an acylphosphine oxide-based photoinitiator(produced by IGM RESINS: Omnirad 819) was used.

In each of the test examples, the “volume ratio of the inorganic solidto the ink total amount,” the “volume ratio of the inorganic pigment tothe inorganic solid,” and the “volume ratio of the inorganic pigment tothe photoinitiator” were calculated. The “volume ratio of the inorganicsolid to the ink total amount” is a value in the case where the inktotal amount is 100 volume %, and the “volume ratio of the inorganicpigment to the inorganic solid” is a value in the case where the totalamount of the inorganic solid is 100 volume %. The “volume ratio of theinorganic pigment to the photoinitiator” is a value (multiple) obtainedby dividing the volume of the inorganic pigment by the volume of thephotoinitiator.

<Evaluation Test>

(1) Ink Viscosity Evaluation

A prepared ink viscosity of each example was measured with a type-Bviscometer. In the measurement, the ink temperature was set at 25° C.,and the rotation speed of a spindle was set at 5 rpm. An ink having aviscosity less than 70 mPa·s was evaluated as “good,” an ink having aviscosity of 70 mPa·s or more and less than 110 mPa·s was evaluated as“acceptable,” and an ink having a viscosity of 110 mPa·s or more wasevaluated as “unacceptable.” Tables 1 and 2 show valuation results.

(2) Printing of Image

The ink of each example was printed on the surface of a glass substrate(softening point: 820° C.) with a thickness of 5 mm. Specifically, theink was ejected onto the surface of the glass substrate with an inkjetapparatus (produced by FUJIFILM Corporation: material printer(DMP-2831)), and then irradiated with UV light (wavelength: 395 nm) forone second, thereby drawing an image with a thickness of 5 to 50 μm onthe surface of the glass substrate. The glass substrate was thencalcined at 700° C., thereby producing a glass product with a decorationpart.

(3) Fixing Evaluation

An adhesion strength of the decoration part after calcination wasmeasured to evaluate a fixing property of ink to the glass substrate.Specifically, in conformity with JIS K5600-5-4, a scratch hardness testwith a pencil method was conducted on the decoration part. A case wherea pencil hardness of the decoration part was 3H or more was evaluated as“good,” and a case where the pencil hardness was less than 3H wasevaluated as “unacceptable.” Tables 1 and 2 show valuation results.

(4) Concealability Evaluation

Concealability of the decoration part formed on the glass substrate wasevaluated by visual observation. Specifically, a paper sheet withwritten characters was placed on the bottom side of the glass substrate,and the decoration part was observed from the written side. A case whereno characters were seen was evaluated as “good,” a case where thecharacters were visible but cannot be read was evaluated as“acceptable,” and a case where the decoration part was transparentenough to read characters therethrough was evaluated as “unacceptable.”Tables 1 and 2 show valuation results.

(5) UV Curing Evaluation

Here, UV curing of ink after UV radiation and before calcination wasevaluated. Specifically, a wipe was lightly pressed against theUV-irradiated glass substrate. A case where no ink was transferred tothe wipe was evaluated as “good,” a case where a small amount of ink wastransferred to the wipe but appearance of an image has no disturbance(blurring) was evaluated as “acceptable,” and a case where a largeamount of ink was transferred to the wipe and appearance of an image hasdisturbance was evaluated as “unacceptable.” Tables 1 and 2 showvaluation results.

TABLE 1 EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE 5 COMPOSITIONPIGMENT YELLOW 4.0 5.5 7.5 10.0 — (VOLUME %) CYAN — — — — 10.0 WHITE — —— — — GLASS FRIT 16.0 14.5 12.5 10.0 10.0 DISPERSER 10.8 10.8 10.8 10.810.8 PHOTOCURABLE MONOMER 66.6 66.6 66.6 66.6 67.8 PHOTOINITIATOR 2.32.3 2.3 2.3 1.2 POLYMERIZATION INHIBITOR 0.2 0.2 0.2 0.2 0.2 TOTAL 100.099.9 99.9 99.9 100.0 VOLUME RATIO OF INORGANIC SOLID 20.0 20.0 20.0 20.020.0 TO INK TOTAL AMOUNT (VOLUME %) VOLUME RATIO OF INORGANIC PIGMENT20.0 27.5 37.5 50.0 50.0 TO INORGANIC SOLID (VOLUME %) VOLUME RATIO(MULTIPLE) OF INORGANIC 1.7 2.4 3.3 4.3 8.3 PIGMENT TO PHOTOINITIATOREVALUATION INK VISCOSITY GOOD GOOD GOOD GOOD GOOD FIXING PROPERTY GOODGOOD GOOD GOOD GOOD CONCEALABILITY ACCEPTABLE GOOD GOOD GOOD GOODPHOTOCURING PROPERTY GOOD GOOD GOOD GOOD GOOD TOTAL EVALUATIONACCEPTABLE GOOD GOOD GOOD GOOD EXAMPLE 6 EXAMPLE 7 EXAMPLE 8 EXAMPLE 9COMPOSITION PIGMENT YELLOW 10.3 10.0 — 8.3 (VOLUME %) CYAN — — 9.7 —WHITE — — — — GLASS FRIT 10.3 10.0 9.7 21.8 DISPERSER 5.5 10.8 13.1 14.7PHOTOCURABLE MONOMER 68.6 65.5 66.0 52.8 PHOTOINITIATOR 5.1 3.5 1.2 2.3POLYMERIZATION INHIBITOR 0.2 0.2 0.2 0.2 TOTAL 100.0 100.0 99.9 100.1VOLUME RATIO OF INORGANIC SOLID 20.6 20.0 19.4 30.1 TO INK TOTAL AMOUNT(VOLUME %) VOLUME RATIO OF INORGANIC PIGMENT 50.0 50.0 50.0 27.6 TOINORGANIC SOLID (VOLUME %) VOLUME RATIO (MULTIPLE) OF INORGANIC 2.0 2.98.1 3.6 PIGMENT TO PHOTOINITIATOR EVALUATION INK VISCOSITY GOOD GOODGOOD ACCEPTABLE FIXING PROPERTY GOOD GOOD GOOD GOOD CONCEALABILITY GOODGOOD GOOD GOOD PHOTOCURING PROPERTY GOOD GOOD GOOD GOOD TOTAL EVALUATIONGOOD GOOD GOOD ACCEPTABLE

TABLE 2 EXAMPLE 10 EXAMPLE 11 EXAMPLE 12 EXAMPLE 13 EXAMPLE 14COMPOSITION PIGMENT YELLOW — 6.0 — — — (VOLUME %) CYAN 17.5 — — — 3.0WHITE — — 16.9 3.0 — GLASS FRIT 7.5 10.0 3.0 17.0 12.0 DISPERSER 14.48.1 16.9 12.3 7.2 PHOTOCURABLE MONOMER 58.7 75.0 60.8 65.1 67.6PHOTOINITIATOR 1.8 0.6 2.1 2.3 10.0 POLYMERIZATION INHIBITOR 0.2 0.2 0.20.2 0.2 TOTAL 100.0 99.9 99.9 99.9 100.0 VOLUME RATIO OF INORGANIC SOLID25.0 16.0 19.9 20.0 15.0 TO INK TOTAL AMOUNT (VOLUME %) VOLUME RATIO OFINORGANIC PIGMENT 70.0 37.5 84.9 15.2 20.0 TO INORGANIC SOLID (VOLUME %)VOLUME RATIO (MULTIPLE) OF INORGANIC 9.7 10.0 8.0 1.3 0.3 PIGMENT TOPHOTOINITIATOR EVALUATION INK VISCOSITY GOOD GOOD GOOD GOOD GOOD FIXINGPROPERTY GOOD GOOD GOOD GOOD GOOD CONCEALABILITY GOOD GOOD GOODACCEPTABLE ACCEPTABLE PHOTOCURING PROPERTY GOOD ACCEPTABLE GOOD GOODGOOD TOTAL EVALUATION GOOD ACCEPTABLE GOOD ACCEPTABLE ACCEPTABLE EXAMPLE15 EXAMPLE 16 EXAMPLE 17 EXAMPLE 18 COMPOSITION PIGMENT YELLOW 2.6 — —9.7 (VOLUME %) CYAN — 14.0 — — WHITE — — 18.0 — GLASS FRIT 17.4 6.0 2.025.5 DISPERSER 10.8 10.8 17.3 17.3 PHOTOCURABLE MONOMER 66.6 67.8 60.445.1 PHOTOINITIATOR 2.3 1.2 2.1 2.3 POLYMERIZATION INHIBITOR 0.2 0.2 0.20.2 TOTAL 99.9 100.0 100.0 100.1 VOLUME RATIO OF INORGANIC SOLID 20.020.0 20.0 35.2 TO INK TOTAL AMOUNT (VOLUME %) VOLUME RATIO OF INORGANICPIGMENT 12.9 70.0 90.0 27.5 TO INORGANIC SOLID (VOLUME %) VOLUME RATIO(MULTIPLE) OF INORGANIC 1.1 11.7 8.6 4.2 PIGMENT TO PHOTOINITIATOREVALUATION INK VISCOSITY GOOD GOOD GOOD UNACCEPTABLE FIXING PROPERTYGOOD GOOD UNACCEPTABLE — CONCEALABILITY UNACCEPTABLE GOOD GOOD —PHOTOCURING PROPERTY GOOD UNACCEPTABLE GOOD — TOTAL EVALUATIONUNACCEPTABLE UNACCEPTABLE UNACCEPTABLE UNACCEPTABLE

As shown in Tables 1 and 2, in Examples 1 through 14, evaluation resultson ink viscosity, adhesion strength, concealability, and photocuringproperty are “acceptable” or more. This shows that an ink with theseproperties improved in a good balance can be prepared by setting thevolume ratio of the inorganic solid to the ink total amount at 35 volume% or less, the volume ratio of the inorganic pigment to the inorganicsolid at 15 volume % or more and less than 90 volume %, and the volumeratio of the inorganic pigment to the photoinitiator at 11 times orless.

Specific examples of the present disclosure have been described indetail hereinbefore, but are merely illustrative examples, and are notintended to limit the scope of claims. The techniques described in thescope of claims include various modifications and changes of the aboveexemplified specific examples.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1 inkjet apparatus    -   10 inkjet head    -   12 case    -   13 storage    -   15 liquid feeding path    -   16 ejection part    -   17 ejection orifice    -   18 piezoelectric device    -   20 guide shaft    -   30 UV irradiator    -   40 printing cartridge    -   100 stirring mill    -   110 supply port    -   120 stirring vessel    -   132 stirring blade    -   134 shaft    -   140 filter    -   150 ejection port    -   A liquid feeding direction    -   X axial direction of guide shaft    -   Y vertical direction of guide shaft

1. An inkjet ink for a glass substrate, the inkjet ink configured foruse in drawing an image on a transparent glass substrate, the inkjet inkcomprising: an inorganic solid including an inorganic pigment and aglass frit, the inorganic pigment configured for use in developing anycolor except for black; a monomer component having a photocuringproperty; and a photoinitiator, wherein: a volume ratio of the inorganicsolid in a case where a total volume of the inkjet ink is 100 volume %is 35 volume % or less, a volume ratio of the inorganic pigment in thecase where the total volume of the inorganic solid is 100 volume % is 15volume % or more and less than 90 volume %, and a volume ratio of theinorganic pigment to the photoinitiator is 11 times or less.
 2. Theinkjet ink according to claim 1, wherein the inorganic pigment is aninorganic pigment that develops a color of cyan, magenta, or yellow. 3.The inkjet ink according to claim 1, wherein the volume ratio of theinorganic solid in the case where the total volume of the inkjet ink is100 volume % is 15 volume % or more and 30 volume % or less.
 4. Theinkjet ink according to claim 1, wherein the volume ratio of theinorganic pigment in the case where the total volume of the inorganicsolid is 100 volume % is 25 volume % or more and 85 volume % or less. 5.The inkjet ink according to claim 1, wherein the volume ratio of theinorganic pigment to the photoinitiator is 10.7 times or less.
 6. Theinkjet ink according to claim 1, wherein the monomer component includesat least: a monofunctional acrylate monomer including one acryloyl groupor one methacryloyl group in a molecule; a monofunctional N-vinylcompound monomer in which one vinyl group is bound to a nitrogen (N)atom of a nitrogen-containing compound; and a polyfunctional vinyl ethermonomer including at least two vinyl ether groups in a molecule.
 7. Theinkjet ink according to claim 6, wherein a volume ratio of the monomercomponent in the case where the total volume of the inkjet ink is 100volume % is 50 volume % or more and 75 volume % or less.
 8. A method forproducing a glass product having a decoration part, the methodcomprising the steps of: performing inkjet printing on a surface of aglass substrate with the inkjet ink as recited in claim 1; applyingultraviolet rays to the surface of the glass substrate and curing theinkjet ink adhering to the surface of the glass substrate; and calciningthe glass substrate at a maximum calcination temperature of 450° C. to1200° C.
 9. A method for producing transfer paper for a glass substrate,the transfer paper being for use in the glass substrate to be subjectedto calcination, the method comprising the steps of: performing inkjetprinting on a surface of a mount with the inkjet ink as recited in claim1; and applying ultraviolet rays to the surface of the mount and curingthe inkjet ink adhering to the surface of the mount.